This application claims the benefit of Japanese Patent Application No. 10-31992, filed on Jan. 29, 1998, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates generally to an optical pickup and an optical disk drive for reproducing video signals, audio signals, and other data from an optical recording medium and more particularly, to an optical pickup in an optical disk drive for reproducing information on a high-density optical disk having a narrowed track pitch.
2. Description of the Related Art
In recent years, there has been demand for increasing optical disk recording density to facilitate recording vast amounts of information onto a single optical disk. For example, it would be desirable for a full motion picture for high definition television to be stored onto one disk. Attempts have been made to narrow the track on the disk (i.e., decreasing the track pitch), to increase the recording density. However, if an optical disk with a narrowed track pitch is reproduced without reducing the spot size formed on the optical disk, a crosstalk component from adjacent tracks increases, which deteriorates the signal-to-noise ratio of the reproduced signal.
A conventional method for removing the crosstalk is to use three beams. These beams are positioned to hit three adjacent tracks, resulting in three spots. Signals produced from the side spots are subtracted from a signal obtained from the center spot.
As an example, FIG. 13 illustrates a method using three beams, in which center light spot 4 is made to strike a track 2 to read information from track 2. In this scheme, other light spots 5 and 6 are positioned to hit tracks 1 and 3, adjacent to track 2. The center spot 4 primarily includes a signal from track 2, but also contains signals leaking from adjacent tracks 1 and 3. The side spots 5 and 6 mainly contain signals from tracks 1 and 3, respectively. In this method, the amount of light of the crosstalk component from the adjacent tracks to the light spot 4 is different from the amount of light of the signal components from tracks 1 and 3 contained in the side spots 5 and 6. Therefore, the amount of light of the signal components contained in the side spots 5 and 6 is reduced to coincide with the crosstalk component from the adjacent tracks to the center spot 4, and the obtained crosstalk components are subtracted from the signal component contained in the center spot 4.
In FIG. 13, the X-axis direction lies in the direction of tracks and corresponds to the direction of time axis during playback. The Y-axis direction is vertical to the track direction and corresponds to the radial direction of the disk. The light spots 4, 5, and 6 are positioned to hit positions offset from each other, both in the X- and Y-axis directions. Therefore, beams reflected from these spots can travel to mutually spaced detectors on a detector array (not shown). The reflected beams can be separately detected by the detectors spaced from each other. Consequently, the crosstalk component can be removed by subtracting the reflected beams of the side spots 5, 6 from the reflected beam originating from the center spot 4.
The light spots 4, 5, and 6 in FIG. 13 are spaced from each other in the direction of the time axis as well as in the radial direction. Therefore, prior to the subtractive processing for removing the crosstalk, the time offsets of the beams reflected from the light spots 4, 5, and 6 must be corrected for the linear velocity of rotation. However, where certain data is sought on the optical disk, such as for a high speed scan, or where data is read at a constant rotational speed, the linear velocity is not kept constant. Therefore, when the crosstalk component is to be removed, it is necessary to correct varying time offsets of the light spots, increasing the difficulty and complexity in removing the crosstalk component.
Another method for removing offsets of the light spots on the time axis is to arrange the light spots 4, 5, and 6 to be at the same position in the X-axis direction, but this is not effective. The light spots on the recording surface of an optical disk are focused to the diffraction limit. However, the beams reflected from the disk are not focused to the diffraction limit on the light-receiving surface of the detector because various servo signals must be obtained. Consequently, the spacing between the reflected beams on the light-receiving surface of the detector is narrower than the spacing between the light spots on the recording surface. If the track pitch on the recording surface is narrower, the light spots on the recording surface are closer and overlap with each other. In such a case, the beams reflected from the disk further overlap with each other on the light-receiving surface of the detector. In order to remove the crosstalk component, the beams reflected from the light spots must be detected separately. Since the detector cannot separate the overlapping reflected beams, it is impossible to remove the crosstalk component.
Accordingly, the present invention is directed to an improved optical pickup and optical disk drive that substantially obviates one or more of the problems due to the limitations and disadvantages of the related art.
An object of the present invention to provide an optical disk drive for use with a recording medium recorded with a narrow track pitch that removes crosstalk leaking from adjacent tracks, thus permitting signals to be read from the medium with a good signal-to-noise ratio.
According to one aspect of the present invention, there is provided an optical pickup having a light illuminating portion for illuminating a plurality of light beams having different wavefronts onto a recording surface of the recording medium to create a plurality of light spots, including a first light spot and a second light spot, the first and second light spots at least partially overlapping with each other, and a detector for receiving light beams reflected by the recording medium, the detector having a first light-receiving surface for receiving reflected light of the first light spot and a second light-receiving surface for receiving reflected light of the second light spot.
According to another aspect of the present invention, there is provided a optical disk drive having a optical pickup including a light illuminating portion for illuminating a plurality of light beams having different wavefronts onto a recording surface of the recording medium to create a plurality of light spots including a first light spot and a second light spot, the first and second light spots at least partially overlapping with each other, and a detector for receiving light beams reflected by the recording medium, the detector having a first light-receiving surface for receiving reflected light of the first light spot and a second light-receiving surface for receiving reflected light of the second light spot, and operation means for obtaining a signal representing information recorded on the recording medium based on a first output signal from the first light-receiving surface and a second output signal from the second light receiving surface.
Other objects and features of the invention will appear in the course of the description thereof, which follows.